This invention relates to a coordinates detecting device for detecting the position of a pen, cursor or the like on a tablet.
A coordinates detecting device comprises: an electromagnetic device such as a pen, cursor, or the like; means for supplying a sine wave voltage having a predetermined frequency to the electromagnetic device; a tablet in which X-axis conductors and Y-axis conductors are arranged in a periodic pattern; and an arithmetic and control section for processing signals which are provided by the conductors when the electromagnetic device is placed on the tablet, to calculate the position of the electromagnetic device.
The coordinates detecting device will be described with reference to FIG. 1.
FIG. 1 is a block diagram of the coordinates detecting device. In FIG. 1, reference numeral 1 designates a sine wave generating circuit for generating a sine wave having a predetermined frequency; 2, an amplifier for amplifying the sine wave voltage of the sine wave generating circuit 1; 3, a cursor having a resistor 3R and a coil 3L; 4, a tablet in which conductors such as X-axis conductors and Y-axis conductors are arranged in a predetermined pattern; and 5, an arithmetic and control section for processing a signal which is outputted by the tablet 4 when the cursor 3 is placed on the tablet 4.
The conductors arranged in the tablet and their output voltages will be described.
FIG. 2A is a wiring diagram of the X-axis conductors in the tablet, and FIGS. 2B and 2C are waveform diagrams showing voltages inducted in the conductors. FIG. 2 is for the X-axis conductors only. The X-axis conductors as shown in FIG. 2A are made up of a cosine line 6 and a sine line 7. The cosine line 6 and the sine line 7 are equal in the pitch of one period (having a pitch p) and are arranged in such a manner that the sine line 7 is shifted as much as a 1/4 p from the cosime line 6. The ends of the cosine line 6 are connected to terminals a.sub.1 and a.sub.2, and the ends of the sine line 7 are connected to terminals b.sub.1 and b.sub.2. FIGS. 2B and 2C show the voltages which are developed when the cursor 3 is placed on the tablet as shown in FIG. 1. More specifically, FIG. 2B shows the waveform of the voltage Vc which is developed across the terminals a.sub.1 and a.sub.2 of the cosine line 6, and FIG. 2C shows the waveform of the voltage Vs which is developed across the terminals b.sub.1 and b.sub.2 of the sine line 7. These voltages are applied to the arithmetic and control section, where they are subjected to arithmetic processing, so that the abscissa of the cursor 3 is calculated. The operation and control for the calculation are carried out in a conventional manner.
In the above-described coordinates detecting device, the arithmetic and control section 5 may perform the arithmetic processing correctly; however, the detection values unavoidably include errors. In order to eliminate this difficulty, heretofore a method is employed in which the accuracies at a number of positions on the entire surface of the tablet are actually measured, and detection values are corrected according to the accuracies thus measured. However, the method is still disadvantageous in that, if the number of positions to be measured is increased, the number of correction data is increased, and if the number of positions to be measured is decreased, the detection accuracy is decreased.